We often tell expecting mums who ask "Should I take supplements Doc? Which one do you recommend?" that "they are all the same...", but are they?

We now know unequivocally that folic acid reduces risk of neural tube defects (NTD) by 92%..The NHMRC has recommended that women of childbearing age take 0.5mg of folic acid daily for at least 1 month before and 3 months into the pregnancy. The recommended dosage is 5mg/day for women at high risk (spina bifida patient, previous child or close relative with NTD, or on anti-epileptics).

The Cochrane meta-analysis of 13 trials in 2006 has concluded that calcium supplement of at least 1g daily in pregnancy halves the risk of pre-eclampsia, reduces the risk of preterm birth. However, it must be pointed out the trial populations have much lower calcium intake than average Australian. Furthermore most pregnancy supplements have much less calcium per tablet than the doses used in these trials. 

There is emerging evidence linking Vit-D deficiency to pre-eclampsia, operative and preterm delivery. A recent research article in MJA has concluded that low Vit-D levels are associated with poorer glycaemic control in gestational diabetics. Interestingly, this study from sunburnt Australia reported a 41% incidence of vit-D insufficiency. Admittedly the reference range for vit-D insufficiency is still debatable, most agree with a serum vit-D level ? 50nmol/l as insufficient. The recommended daily doses of Vit-D are 1000 to 2000IU (25-50 ?g).

Iodine deficiency has been associated with higher incidence of stillbirths, miscarriages, congenital abnormalities in fetus, and early brain development abnormality, mental defects, increased mortality in neonate. The NHMRC recommends that all women who are pregnant, breastfeeding or considering pregnancy take an iodine supplement of 150?g/day.

In 2004 the US Food & Drug Association and ACOG advised all pregnant women to limit fetal exposure to mercury by  limiting seafood consumption to 340g/week. Seafood is a primary source of omega-3, which has been shown to improved fetal brain and eye development in observational studies. The postulated benefits of Omega-3 in preterm birth and peripartum depression is less clear.

Cochrane meta-analysis of 9 trials concluded that Vitamin C &  E do not decrease the risk of pre-eclampsia but may in fact increased the risk of gestational hypertension. Another Cochrane systemic review of 28 trial in 2005 showed that taking any vitamins prior to pregnancy or in early pregnancy does not prevent miscarriage or stillbirth, but increases the incidence of twin pregnancy. 

About 10% of pregnant women develop iron deficiency anaemia in Australia. Anaemia increases the risk of preterm delivery and low birth weight. But high maternal iron levels are associated with fetal growth restriction, preterm delivery, preeclampsia and are also linked to gestational diabetes. Moreover, anaemia may be due to other causes, e.g. Vit-B12 deficiency (pernicious anaemia, vegan), Thalassemia, or physiological dilution due to increase intravascular volume in pregnancy. It is therefore prudent to confirm iron deficiency before giving iron supplementation in large doses.

In summary, the current consensus is perinatal supplementation of Iodine, Vit-D and Folic acid are recommended. Omega-3 and calcium are beneficial and vitamin C & E are not. Large doses of iron supplement should be used more selectively. As for the answer to "Which one would you recommend?", I have compiled a comparison table:

Disclaimer: I declare that I have no competing interests in any pregnancy supplement products.